20.1. Typical bearing failures
2. Bearing failure occurs due to insufficient lubrication, dirt and other foreign particles, engine overload and corrosion. Regardless of the cause of bearing failure, it must be corrected before engine assembly to prevent recurrence.
3. When inspecting the bearings, remove them from the cylinder block, main bearing caps, connecting rods and connecting rod caps and lay them out on a clean surface according to their position in the engine. This will allow you to associate the condition of the bearings with the corresponding crankshaft journals.
4. Dirt and other foreign particles enter the engine in a variety of ways. They may be left in the engine during assembly or enter through filters or the PCV system. They may enter the oil and from there into the bearings. Often there are chips from machining and normal wear in the engine. Abrasive particles are sometimes left in the engine after rebuilds, especially when parts are not cleaned properly. Whatever the source, these foreign particles often become embedded in the soft bearing material and are not recognized. Large particles do not become embedded in the bearings and will scratch the bearing material and journals. The best way to prevent this cause of bearing failure is to maintain cleanliness during engine assembly. Frequent and regular engine oil changes are also recommended.
5. Insufficient lubrication (or poor lubrication system) has several interrelated causes. Overheating (causing the oil to become thinner), overloading (causing oil to be squeezed out of the bearing surfaces), and oil leakage or overflow (due to large bearing clearances, worn oil pumps, or high engine speeds) all contribute to poor lubrication system performance. Obstruction of oil passages, which is usually the result of misalignment of the oil holes in the bearing shells, leads to insufficient lubrication of the bearings and their failure. When insufficient lubrication leads to bearing failure, the bearing steel backing material is abraded or worn away. The temperature may rise to the point that the steel backing turns blue from overheating.
6. Driving style can also affect bearing life. Driving with the throttle fully open, driving at low speeds (overloading the engine) lead to very high loads on the bearings, which causes a decrease in the thickness of the oil film. Such loads cause the bearings to bend, which leads to the formation of small cracks on the bearing surfaces (fatigue damage). Over time, the bearing material wears away and exposes the steel base. Short trips cause corrosion of bearings, since the engine does not warm up sufficiently to remove condensed water and corrosive gases. These products accumulate in the engine oil, forming acid and sticky deposits. When such oil enters the bearings, the acid causes corrosion of the material.
7. Incorrect installation of bearings during engine assembly also leads to bearing failure. Too tight tightening of bearings leads to a decrease in the lubrication gap and to stagnation of oil. Dirt or foreign particles accumulated behind the bearing shell lead to the formation of stains on the bearing and its failure.